For fuel pipelines of automobiles, a metallic tube-shaped body had been employed. The surface of the metallic tube-shaped body was covered with plating or a resin in a multiple form to reinforce it in corrosion resistance or chemical resistance.
However, in recent years, as tube-shaped bodies for fuel pipelines, resin tube-shaped bodies have been employed as well as metallic tube-shaped bodies.
Unlike metallic tube-shaped bodies, resin tube-shaped bodies have various advantages such as being resistant to rusting, light in weight, easy in processing and highly flexible in designing. Accordingly, the resin tube-shaped bodies are highly advantageous in automobile field for which low fuel consumption and weight saving have been pursued.
On the other hand, the resin tube-shaped bodies are low in heat resistance as compared with metallic tube-shaped bodies. Therefore, as the mainstream when used for tube-shaped bodies for fuel pipelines, the resin tube-shaped bodies have been used for fuel tank side and the metallic tube-shaped bodies have been used for the inside of engine room as the primary heat source.
However, a demand has recently been increased to use the resin tube-shaped bodies for engine room as well in view of the above-mentioned properties, and for this purpose, improvement of heat resistance is a pressing need, and therefore various proposals have been made.
It has conventionally been known that Polyamide 11, (PA11) (undecanlactam) or Polyamide 12, (PA12) (lauriclactam) is used for the most-outer layer of a resin tube-shaped body. However, both are low in heat resistance and has low reliability in heat resistance in an atmosphere at 100° C. or higher. Accordingly, a method has been employed which covers the resin tube-shaped bodies with a protector made of ethylene/propylene/diene rubber (EPDM). EPDM of this protector is thermosetting and therefore excellent in heat resistance, but it is rubber and therefore poor in lubricating properties with the surface of the resin tube-shaped body when the protector is installed. Accordingly, it has been required to have such a structure that a gap be formed between the protector and the resin tube-shaped body, and it has further been required to take cumbersome treatment of coating the surface of the resin tube-shaped body with a lubricant such as silicone at the time of installation. Further, by the installation of the protector, problems such as increase of weight and cost increase have been caused.
After that, various proposals have been made in order to obtain heat resistant resin tube-shaped bodies without using a protector. The applicant provided in the past the one having heat resistance improved by providing an expandable PET (polyethylene terephthalate) resin layer on the main resin tube-shaped body made of a thermoplastic resin, and then providing an inflammable PET resin layer thereon. (Patent Document 1)